JMeter pass JSON response value to next request - testing

Question

I am using JMETER to test a web app.
First I perform a http GET request which returns a JSON array such as:
[
{
"key1":
{
"subKey":
[
9.120968,
39.255417
]
},
key2 : 1
},
{
"key1":
{
"subKey":
[
9.123852,
39.243237
]
},
key2 : 10
}
]
Basically I want to take randomly one element, take the elements of key1 and create 2 variables in JMeter that will be used for the next query (if randomly it is not possible than just the 1st element).
I tried using JSON Extractor with the following settings (the example shows a single variable case):
and in the next http GET request referencing the parameter as ${var1}.
How to set JSON Extractor to extract a value, save into a JMeter variable to be used in the next http GET request?

Answer 1

Correct JSON Path query would be something like:
$..key1.subKey[${__Random(0,1,)}]
You need to switch Apply to value either to Main sample only or to Main sample and sub-samples
In the above setup:
Match No: 0 - tells JMeter to get random value from key1 subkey
${__Random(0,1,)} - gets a random element from the array, i.e. 9.120968 or 39.255417
More information:
Jayway Jsonpath
API Testing With JMeter and the JSON Extractor

Answer 2

"JMeter variable name to use" option that you've switched on there means that you'd be examining the content of this variable INSTEAD of Sample result.
So the fix is obvious: if you intend to extract whatever you extracting from Sample result - change it back to it.
PS If you intend the opposite (process the variable content, not the sample result) - let me know please.